The present invention relates to combine harvesters and has particular reference to such machines having rotary separating mechanisms.
In known combine harvesters, grain is threshed and separated in a threshing and separating mechanism and the separated grain, together with the impurities, such as chaff, dust, straw particles, and tailings, is fed to a cleaning mechanism for cleaning. Clean grain is collected below the cleaning mechanism and fed to a grain tank for temporary storage. The tailings are separated from the clean grain and impurities for reprocessing. This reprocessing either involves recycling the tailings through the threshing and separating mechanism or treating them in a separate tailings rethreshing means.
While the terms "grain", "straw", and "tailings" are used principally throughout this specification for convenience, it should be understood that these terms are not intended to be limiting. Thus "grain" refers to that part of the crop which is threshed and separated from the discardable part of the crop material which is referred to as "straw". Incompletely threshed ears are referred to as "tailings".
Recent developments in combine harvesters have led to so called rotary machines wherein both threshing and separating are accomplished in mechanisms comprising rotary components cooperable with respective stationary threshing and separating concaves and grates. In conventional combine harvesters, grain separation is accomplished by straw walkers. In rotary combines the crop material is subjected to a much more aggressive and positive separating action during a relatively prolonged period of time, whereby the efficiency of a rotary combine harvester usually is greater than that of a conventional machine.
Several types of rotary combine harvesters have appeared on the market and in one such machine, a conventional transversely-extending threshing mechanism having a threshing cylinder and a cooperable concave is combined with a rotary separating mechanism having a rotor of a width greater than that of the threshing mechanism, and disposed parallel thereto with its ends extending transversely past the respective ends of the threshing mechanism. The rotary separating mechanism operates spirally to convey the crop material received from the threshing mechanism towards each of its ends, while submitting the crop to a separating action. With such a separating mechanism, the incoming layer of crop material has to be divided in two substantially equal portions, each of which is then spirally conveyed from the center of the separating mechanism to one or the other of its ends.
Most modern combine harvesters are fitted with grain loss monitoring devices in order to ascertain, as accurately as these devices permit, the amount of grain being discharged from the machine with the straw and hence being lost. The grain loss monitoring devices comprise grain sensors which are normally mounted in the path of the crop material (grain mixed with straw) being discharged from the machine and each sensor is tuned to respond to impacts by the grain kernels to produce an electrical output signal representative of the number of impacts and hence representative of the grain being lost. Two main problems arise with this location of the grain sensors, the first being that pieces of straw tend to hook around the sensors and/or their mountings possibly resulting in plugging or blocking of the machine, and the second being that, in rotary combines, pieces of straw impacting on the sensor by virtue of the increased velocity thereof in being discharged from the separator mechanism may well produce output signals from the sensors.